1. Field of the Invention
This invention relates to an apparatus for inspecting electronic devices mounted on a circuit board, and more particularly to an apparatus for performing a visual inspection of the condition of mounting an electronic device on a circuit board.
2. Description of the Prior Art
Various apparatus for inspecting an electronic device mounted on a cricuit board for positional deviation, lifting, solder condition, etc. have been proposed. A typical example of such apparatus is proposed in Japanese Laid-Open Patent Publication (Kokai) No. Heisei 1(1989)-79874. This apparatus comprises an upper or top camera for observing the electronic parts from a perpendicular direction above and a plurality of side cameras each for observing from an angle above, so that the upper camera can inspect deviation in position of the electronic devices, missing devices, etc., and the side cameras can inspect the degree of lift of the electronic devices from the circuit board.
The prior art apparatus comprising a combination of the upper camera and side cameras as described above has many advantages: it can inspect a wide area of a circuit board at one time; it can perform a relatively large number of inspection items; and its inspection speed is fast. Since the cameras can only detect two-dimensional planar data and not height data, however, this apparatus cannot perform special kinds of visual inspection items such as recognition of the shape of solder fillets which requires precise height data.